Starter system of an internal combustion engine



Dec. 29, 1964 Filed May 11.

E. KEUCHEN ETAL 3,163,769

STARTER SYSTEM OF AN INTERNAL COMBUSTION ENGINE 1960 2 Sheets-Sheet 1 Dec. 29, 1964 E. KEUCHEN ETAL 3,163,769

STARTER SYSTEM OF AN INTERNAL COMBUSTION ENGINE 2 Sheets-Sheet 2 Filed May 11, 1960 HI- F United States Patent 3,]lti3fi69 STARTER SYSTEM or AN ll lT-SERNAL Ctlhdlllld'lilifll l ENGINE Erich lhleuchen, Aachen, and Wilhelm Haven, Wuerselen,

Germany, assignors to @arhe, Lahrneyer dz (Io. Ahtiengeseilschatt, Aachen, Germany Filed May 11, 196i), Ser. No. 28,255 (Claims priority, application Germany May 14, M59 13 Claims. (Cl. 290-43) The present invention concerns a. starter system of an internal combustion engine, and more particularly, a system incorporating a safety device for preventing the operation of the starter means under undesirable conditions.

it is of great importance to protect the starter, i.e. the starter motor and the pertaining gears, against being rotated at excessive speeds which could easily occur if the starter is disconnected too late. On the other hand, it is necessary to prevent the possibility of unintentionally operating the starter while the engine is operating normally because this may easily lead to destruction of elements of the starter arrangement and particularly of the gears. it is further desirable to limit the starter operation to that period of time only which is necessary for starting the engine because in this manner the life of those parts of the starter arrangement which are subject to wear is greatly increase It has been proposed in the past to provide the starter systems with safety devices for preventing the above mentioned inconveniences. However, an entirely satisfactory solution has not yet been proposed. For instance, if such a safety device is made to be operative in response to the magnitude of the oil pressure produced by the rotation of the engine, the operation of the starter device during regular operation of the engine can be avoided. However, whenever the time required for starting the engine, e.g. at low temperatures, or in the case of repeated misliring, is comparatively long, then already during the operation of the starter motor, and before the operational start of the engine itself, an oil pressure may develop of such a magnitude that hereby the starting operation is interrupted by the safety device. Thus, starting of the engine would be rendered rather diflicult or even impossible. If the safety device were to be operated in response to a vacuum created in the carburetor, other difticulties develop because the above mentioned vacuum is extremely low as long as the engine operates at very slow speed.

Even if the safety device would be operated by the voltage output of the lighting generator an undesired operation of the starter would not be safely prevented during the operating period of the engine because the lighting generator usually does not furnish a voltage of substantial amplitude as long as the engine runs at idling speed.

it is therefore a main object of this invention to provide for a starter system in which all the above ditficulties are safely avoided.

According to the invention the just mentioned dithculties are safely avoided due to the fact that in the system according to the invention an operation of the starter after the start of the operation of the engine is automatically prevented and an effective operation of the starter remains blocked until the engine comes again to "ice a standstill. For this purpose the operativeness of the starter control elements depends on two factors characterizing the actual operating condition of the engine.

Preferably, the two factors characterizing the actual operating condition of the engine are selected in such a manner that one of these factors undergoes change of its magnitude while the engine rotates at the lowest speeds, while the other factor undergoes a substantial variation of its magnitude while the engine runs at idling speed or at speeds higher than this idling speed.

Preferably, the system is so arranged that the starter motor can be operated via the respective starter control means only when both said two factors characterizing the operating condition of the engine assume a value corresponding substantially to standstill condition of the engine, and that the automatic disconnection of the starter arrangement is effected when both said factors reach a value which corresponds to normal safe operation of the engine.

011 the other hand, it is also advisable to provide for a system in which the operation of the starter via the starter control means is made dependent upon the fact that the one factor which undergoes a substantial variation in the range of low speeds does not reach a value which corresponds to the normal speed and operation of the engine. The thus obtained condition of the starter control means is then maintained until also the second factor exceeds the value which corresponds to the normal operating condition of the engine, or until the starter switch is returned to its off position.

With above objects in view a stanter system for an internal combustion engine having parts moving accordingly to varying speeds of the engine, comprises, according .to the invention, in combination, a main starter circuit including starter means for starting the engine; operating means for operating said starter means; electrically operable actuating switch means capable of operatively connecting said starter means with said operating means by closing said main starter circuit; a control circuit including main starter switch means and an electrically controllable switching device in circuit with said electrically operable actuating switch means and changeable between circuit opening condition and circuit closing condition for operating said actuating switch means; and combined control means actuated by said moving parts of the engine (a) for automatically changing said electrically controllable switching means from circuit opening to circuit closing condition when said main starter switch means is operated while the speed of the engine is below a first predetermined value, (b) for automatically maintaining said electrically controllable switching means in circuit closing condition after the same has been changed to such circuit closing condition, as long as said main starter switch is being operated and the speed of the engine is above said first predetermined value and remains below a second predetermined value higher than said first value, without being capable of changing said electrically controllable switching means from circuit opening to circuit closing condition while the speed of the engine is between said first and second predetermined values, and (c) for automatically changing said electrically controllable switching means from circuit closing to circuit opening condition when the speed of the engine reaches and exceeds said second predetermined value.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a circuit diagram illustrating a starter system according to the invention comprising a safety relay equipped with two separate windings; and

FIG. 2 is a similar circuit diagram illustrating a second embodiment of the invention comprising a safety relay equipped with only one winding.

Referring now to FIG. 1, the starting means 12 comprise a main starter circuit including a starter motor M operable by a battery 4 via electrically operable actuating switch means represented by a starter relay 13, upon operation of the main starter switch 1 which comprises a movable contact as shown cooperating with two stationary contacts 2 and 3. A safety relay 7 representing generally an electrical switching device is connected in circuit between the switch contact 3 and the relay 13. The relay '7 is equipped with two stationary contacts 11 respectively connected with the contact 3 and the relay 13, which contacts may be connected by the armature member' 10 whenever the windings 3 and 9 of the relay '7 are energized. The operation of the safety relay 7 is controlled by combined control means which comprise for instance a switch a connected between ground and the winding 8 and normally closed, the contacts being separated in response to oil pressure applied to the device 6. In a generally well known manner one of the contacts of the switch 6 is attached to a diaphragm as shown. The second winding 9 of the relay 7 is connected in series wit-h the lighting generator G forming part of the lighting generator equipment 14 and having a shunt coil 15.

An auxiliary circuit connects the contact 2 of the main starter switch 1 with the oil pressure control switch 6 and comprises a signal light 5.

For initiating the starting procedure the movable contact arm of the main starter switch (which may be com bined with the ignition switch) is turned in a counterclockwise direction two steps so that the positive terminal of the battery 4, the negative terminal of which is conhected to ground, is simultaneously connected with the contacts 2 and 3. As soon as battery voltage is applied to the contact 2, the control light is caused to give a visible signal. Assuming that the engine was at a standstill, no oil pressure is produced thereby yet so that the contacts of the switch 6 are in closed position so that a circuit is established from the positive terminal of the battery 4 via main switch 1, contact 2 and control light 5 to the switch 6 and back to the negative terminal of the battery 4.

However, the movable contact arm of the main switch 1 establishes also via contact 3 a circuit to the left-hand contact 11 of the relay 7 and from there through both windings 8 and 9 to ground. Thus, both windings 8 and 9' are energized. The winding 8 is placed in circuit via the closed contacts of the switch 6, while the winding 9 is in circuit across the generator G because the latter, being at standstill, still has the same potential as ground.

The windings 3 and g are so dimensioned that the relay 7 is actuated, i.e. the armature 10 is attracted into contact closing position, only when both coils 3 and 9 are supplied with full potential. However, thereafter the armature 10 will be held in contact closing position even if only the Winding 9 is energized. By the movement of the armature 10 into con-tact closing position, the circuit for the relay 13 is closed via the main switch 1 and the contacts 11. Upon actuation of the relay 13 the main starter circuit is closed and the starter motor M is energized. Upon operation of the motor M the latter is coupled in the well known manner via conventional gears with the engine,

not shown, so that the shaft of the latter is rotated. Now, the oil pump of the engine starts delivery and gradually builds up a sufiicient oil pressure for operating the switch 6 whereby the contacts of that switch are separated from each other. Consequently, the signal light 5 is extinguished and the winding 8 of the safety relay 7 is de-energized. However, the holding winding 9 remains energized across the armature of the lighting generator arrangement 14 so that the armature to of the safety relay '7 remains in contact closing position and the circuit between the main switch 1 and the relay 13 remains closed via the contact 11. Thus, the starting procedure is further continued.

As now the rotary speed of the engine increases the voltage output of the lighting generator arrangement 14 increases likewise. As can be seen, the polarities of the voltages furnished from the battery 4 and from the genorator arrangement 14 to the winding 9 are opposed to each other. Thus, with increasing output voltage of the lighting generator arrangement 14, the energy supplied to the winding 9 for the purpose of energization is reduced.

As soon as the engine is actually started, the rotary speed thereof is further increased until the ordinary idling speed is reached, or even exceeded. Under these circumstances the voltage output of the lighting generatorarrangement 14 *further increases and exceeds, in counteraction agm'nst the voltage supplied by the battery 4, that critical voltage value which is the minimum requirement for the energization of the winding 9 sufficient for holding the armature 14 in contact closing position. Thus, the armature it) is moved by return means, not shown, to circuit opening position whereby the supply circuit for the starter relay 13 is interrupted, and the entire starter arrangement 12 is rendered inoperative. The starter motor M is disconnected from the engine so that the starter arrangement 12 is not exposed any more toundue wear due to extended operation or due toexcessive speeds of the engine.

Of course, the possibility still exists to discontinue the starter operation arbitrarily by simply returning the main starter switch 1 to normal off position. Hereby a circuit from the battery to the windings 8 and 9 is interrupted at the contacts 2 and 3 so that also in this case the armature it? would be caused to return to circuit opening position so as to disconnect the starter arrangement 12.

As long as the engine is in regular operation, a repeated operation of the starter arrangement 12 is safely prevented. This is due to the fact that if the main starter switch 1 would be moved again into operative position so as to connect the battery with the contact 3, the windings 8 and 9 of the safety relay 7 would be connected only at one end with the positive terminal of the battery. The opposite ends of the windings 8 and 9, however, remain disconnected because first of all the switch 6 operated by the prevailing oil pressure is in circuit opening condition. It would return to contact closing position only when the oil pressure drops substantially, i.e. when the engine returns to standstill. On the other hand, the winding 9 is still connected across the lighting generator arrangement 14. However, even if the engine speed is reduced to slow idling speed, the output voltage of the generator arrangement 14 drops below the voltage of the battery 4, but the weak energization of the coil 9 under these circumstances would not be suflicient for attracting alone the armature 10 into contactclosing position. Thus, a repeated operation of the starter arrangement by operation of the main starter switch 1 will be possible only after the switch 6 has returned to contact closing position and also the output voltage of the lighting generator arrangement 14 has practically vanished, i.e. when the engine has come to a standstill.

In a modification of the above described embodiment and also understandable from PEG. 1, the windings of the safety relay 7 are so dimensioned that the winding 8 alone is capable of moving the armature ltl into contact closing position when energized. The winding 9 is in this case a plain holding winding. Thus, in this case the starting procedure may be initiated as soon as the oil pressure controlling the pressure switch. as has decreased to such a degree that the contacts or" the switch 6 return to circuit closing position. On the other hand, the termination of the starting procedure depends only on the output voltage of the lighting generator arrangement 14.

In a further modification of the above described bodiment, the line connecting contact 3 with the coils 8 and 9 (or connecting contact 3 of the single coil 16 in FIG. 2) is not connected also to the left-hand contact 11 of the relay '7, This contact is connected directly with the positive terminal of the battery 4. The operation of the devices according to FIGS. 1 and 2 remains exactly the same as otherwise described herein. However, since the currents required for operating the starter arrangement 12 across contacts 11 are rather strong, the just described alternative embodiment relieves the contacts of the main starter switch 1 of these heavy currents whereby the service life of the switch it is greatly extended.

Both in the above described and in the subsequently described embodiments of the invention it is of great advantage that the circuit of one of the windings of the safety relay 7 is connected across the generator G. This has the effect that the current flowing from the main starter switch 1 via the holding winding 9 and via the winding 16, respectively, of the embodiment according to FIG. 2 and through the lighting generator arrangement 14 must pass partly also through the shunt winding 15 of the generator G. This constitutes a separate excitation which will cause even those lighting generators to become excited by means of this separate excitation, so as to furnish an output voltage even at comparatively low rotational speeds even it the collector is contaminated or corroded which otherwise would cause only a belated delivery of output voltage or in certain cases even no output voltage at all.

It is recommended to locate the safety relay 7 in close proximity to the main starter switch 1 because in this case the length of the connecting lines which carry the comparatively heavy currents required by the starter arrangement 12 and therefore causing possibly considerable voltage drops can be kept very short, Further advantages can be derived from arranging the safety relay 7 together with the main starter switch 1 and the ignition switch, not shown, or also the relay 13 of the starter arrangement in close proximity with each other or even compounded structurally into one unit. If in this manner the line resistance in the circuit of the starter relay 13 is reduced, the latter obtains a larger portion of the voltage of the battery 4, and by adjusting the winding of the relay 13 to these conditions the components of this relay 13 are utilized more eificiently and it is possible to substantially reduce its dimensions.

Referring now to the embodiment illustrated by FIG. 2 generally similar to the embodiment of FIG. 1, it can be seen that also in this case the starting procedure is dependent on the oil pressure built up by the operation of the engine and on the output voltage of the lighting generator arrangement 14. In this embodiment the safety relay 7 has only one winding 16. When the main starter switch 1 is moved into contact closing position so as to connect the contact 3 with the positive terminal of the battery 4 while the engine is at standstill, the winding 16 is energized from the positive terminal of the battery 4 via switch 1, contact 3 and the oil pressure switch 6 being in circuit closing condition. Since contact 2 is likewise connected with the battery, the signal lamp 5 is connected in parallel with the winding and therefore is lighted brightly,

sheaves As soon as the shaft of the engine is rotated through the starter action suflicicntly for causing build-up of suflicient oil pressure, the contacts of the oil pressure switch 6 are separated so that now the winding 16 is energized only to a lesser degree. The winding is now connected to ground only across the resistance 17 and the armature ot' the generator G in which gradually a counter voltage is developing. Thus, the brightness of the light from the signal lamp 5, being connected in parallel with the winding 16 is decreased because the current flowing through the lamp 5 is also reduced by the eitect of the resistance 1'7 and the gradually developing counter voltage of the lighting generator arrangement 1%. The starting procedure is terminated as in the preceding embodiment as soon as the output voltage of the lighting generator G reaches a value which counteracts the voltage supply from the battery 4 to such a degree that the resulting potential across the coil 16 drops below the critical value sufficient for holding the armature 1d in contact closing position. It is advantageous to construct the relay 7 in such a manner that an attraction of the armature 10 into contact closing position is obtained only when due to circuit closing condition of the oil pressure switch 6, the full battery voltage is applied to the winding 16, while a weaker holding current may be suh'icient for maintaining the winding 16 in en ergized condition.

In this manner, also in the second embodiment of the invention, the starting procedure is terminated as soon as the internal combustion engine or the lighting generator G connected therewith exceeds a predetermined speed. he starter equipment cannot be switched on again while the engine is running as has been explained above, because even if the main starter switch 1 is moved to a position in which the contacts 2 and 3 are connected with the battery, and excitation of the winding lid can be efifected while the speed of the engine is still at its lowest value, this excitation corresponds only to the potential difference between the battery potential and the output voltage of the generator G. However, this weak excitation is not sufiicient for attracting the armature it! of the relay '7 into contact closing position. Only after the oil pressure produced by the rotation of the engine is reduced and therefore the switch 5 has returned to contact closing position, the winding 16 is energized sufiiciently for attracting the armature Jill and to initiate, by closing the connection between the contacts 11, a new starting procedure via the starter relay 13.

When the main starter switch 1 is moved into a posi tion which connects the battery with the contact 3, the current flowing via the closed oil pressure switch 6 directly to ground causes the signal lamp 5 first of all to light brightly. However, after the oil pressure switch 6 has been caused by rising oil pressure to change to circuit opening position, the current flowing now via the resistance i7 and the armature of the generator G is considerably weaker so that the signal lamp 5 emits much weaker light, and upon closing of the conventional return-current cutout switch, not shown, the lamp 5 is extinguished altogether. Therefore, in this arrangement a separate control or signal lamp for indicating the operative condition of the lighting generator arrangement 14 can be saved. It is advisable in such an arrangement to provide a corresponding arrangement of colored cover glasses for the lamp 5 in order to more strikingly display the diiierenccs in the brightness of the lamp 5.

In the above embodiments of the invention, two factors have been utilized for indicating the varying operating conditions of the engine, namely the corresponding varying values of the oil pressure and of the output voltage of the lighting generator arrangement. In this manner, according to the invention, the operation of the safe ty relay 7 has been made dependent upon two factors representing the operative condition of the engine without necessitating the addition of any new components or an alteration or modification of conventional equipment of the power plant of which the engine is a part. However, it should be understood .that instead of utilizing directly the output voltage of the lighting generator a contact may the arranged in connection with the conventional return-current cutout switch of the lighting generator Control and may be used for indicating depending upon its circuit opening or circuit closing position, the operative condition of the lighting generator and thus that of the engine. Also, a control of the safety relay may be derived from the characteristic of the ignition current which is initially high and drops with increasing speed of the engine whereby also the varying operative conditions of the engine would be indicated. Similarly, also a rotary speed indicator or a control member responding to the vacuum existing in the carburetor in dependence upon the operating condition of the engine may be used in a similar manner.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of stanter systems of an internal combustion engine differing from the types described above.

While the invention has been illustrated and described as embodied in a starter system for an internal com-bustion engine having parts moving in accordance with varying speeds of the engine, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without on itting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a starter system of an internal combustion engine, in combination, starter relay means for starting the engine :when said relay means is energized; an energy supply circuit for said starter relay means including manually operable starter switch means connected between one pole of a source of electric energy and said starter relay means for closing and interrupting said supply circuit for said starter relay means depending upon open and closed position, respectively, of said starter switch means; safety relay means having normally open contact means connected in said supply circuit between said starter switch means and said starter relay means, and having two coil means for moving, when simultaneously energized, said contact means to closed position, said coil means being connected between said starter switch means and the other pole of said source; and combined control means inserted between said coil means and said other pole of said source and being capable of assuming two alternative conditions, in one of which the energization of both said two coil means is effected when said starter switch means is in closed position, while in the other condition the energization of said coil means is prevented, said combined control means assuming said conditions only in response to the simultaneous occurrence of two phenomena characteristic of predetermined operating conditions, respectively, of the engine.

2. In a starter system of an internal combustion engine, in combination, starter relay means for starting the engine when said relay means is energized; an energy supply circuit for said starter relay means including manually operable starter switch means connected between one pole of a source of electric energy and said starter relay means for closing and interrupting said supply circuit for said starter relay means depending upon open and closed position, respectively, of said starter switch means; safety relay means having normally open contact means connected in said supply circuit between said starter switch means and said starter relay means, and having first and second coil means for moving, when simultaneously energized, said contact means to closed position, said second coil means alone being incapable of moving, when energized, said contact means to closed position, but capable of holdring, when energized, said contact means in closed position, said two coil means being inserted between said starter switch means and the other pole of said source; and combined control means connected between said coil means and said other pole of said source and being capable of assuming two alternative conditions, in one of which the energization of both said two coil means is effected when said starter switch means is in closed position, while in the other condition the energization of said two coil means is prevented, said combined control means assuming said conditions only in response to the simultaneous occurrence of two phenomena characteristic of predetermined operating conditions, respectively, of the engine.

3. A starter system of an internal combustion engine according to claim 1, and applying to an engine having means for producing oil pressure substantially proportional to the engine shaft speed, said control means including. first and second control means inserted between said coil means and said other pole of said source, said first control means being capable of applying to one of said two coil means a counteracting potential corresponding to the rotary speed of the engine shaft and of a polarity opposite to that of said source as applied to said one coil means through said starter switch means when in closed position, and said second control means being an oil pressure actuated switch device changeable from a normal circuit closing to a circuit opening position depending upon a predetermined minimum amount of oil pressure applied thereto only during rotation of the engine shaft, said coil means being dimensioned for being fully energizcd by said source upon movement of said starter switch means to closed position only when due to standstill of the engine said counteracting potential is not applied to said one coil means while simultaneously said pressure actuated switch device is due to low oil pressure in circuit closing position, and said coil means being further dimensioned for causing said safety relay contact means to be in open position when said counteracting potential is due to rotation of the engine shaft above a predetermined value while simultaneously said pressure actuated switch device is due to increased oil pressure in circuit opening position thus rendering a movement to closed position of said starter switch means ineffective.

4. A starter system as claimed in claim 3, wherein said safety relay means has a single coil means connected directly with said switch device, and wherein a resistance of predetermined value is connected between said single coil means and said first control means.

5. A starter system as claimed in claim 4, wherein said first control means is a generator means in driving connection with the engine, and wherein said switch device is a pressure switch responsive to pressure derived from the operation of the engine.

6. A starter system as claimed in claim 3, wherein said safety relay means has two separate coil means both connected at one of their respective ends to said starter switch means, the other end of one of said coil means being connected directly to said switch device, the other end of the other one of said coil means being connected to said first control means.

7. A starter system as claimed in claim 6, wherein said first control means is a generator means in driving connection with the engine.

8. A starter system as claimed in claim 4, including a signal means connected in parallel with said single coil means between said starter switch means and a junction 9 point located between said single coil means and said resistance.

9. A starter system as claimed in claim 6, including a signal means connected in parallel with said one of said coil means between said starter switch means and said switch device.

10. A starter system as claimed in claim 8, wherein said signal means is a signal lamp means for indicating by its varying emission of light the potential applied thereto and thereby the operating conditions of the engine.

11. A starter system as claimed in claim 9, wherein said signal means is a signal lamp means for indicating by its varying emission of light the potential applied thereto and thereby the operating conditions of the engine.

12. A starter system as claimed in claim 10, including colored light transmittance means mounted adjacent to said signal lamp for intensifying the indication of vary- 10 ing operating conditions represented by varying brightness of the light emission of said lamp.

13. A starter system as claimed in claim 11, including colored light transmittance means mounted adjacent to said signal lamp for intensifying the indication of varying operating conditions represented by varying brightness of the light emission of said lamp.

References Cited in the file of this patent UNITED STATES PATENTS 1,246,056 Conrad Nov. 13, 1917 1,950,722 Fitz Gerald Mar. 13, 1934 1,989,057 Kongsted Jan. 22, 1935 2,071,042 Maurer Feb. 16, 1937 2,078,608 Maurer Apr. 27, 1937 2,757,295 Briggs July 31, 1956 

1. IN A STARTER SYSTEM OF AN INTERNAL COMBUSTION ENGINE, IN COMBINATION, STARTER RELAY MEANS FOR STARTING THE ENGINE WHEN SAID RELAY MEANS IS ENERGIZED; AN ENERGY SUPPLY CIRCUIT FOR SAID STARTER RELAY MEANS INCLUDING MANUALLY OPERABLE STARTER SWITCH MEANS CONNECTED BETWEEN ONE POLE OF A SOURCE OF ELECTRIC ENERGY AND SAID STARTER RELAY MEANS FOR CLOSING AND INTERRUPTING SAID SUPPLY CIRCUIT FOR SAID STARTER RELAY MEANS DEPENDING UPON OPEN AND CLOSED POSITION, RESPECTIVELY, OF SAID STARTER SWITCH MEANS; SAFETY RELAY MEANS HAVING NORMALLY OPEN CONTACT MEANS CONNECTED IN SAID SUPPLY CIRCUIT BETWEEN SAID STARTER SWITCH MEANS AND SAID STARTER RELAY MEANS, AND HAVING TWO COIL MEANS FOR MOVING, WHEN SIMULTANEOUSLY ENERGIZED, SAID CONTACT MEANS TO CLOSED POSITION, SAID COIL 